Such an exhaust system generally comprises one or more catalytic converter units. For example, a catalytic converter unit directly following the internal combustion engine in an internal combustion engine exhaust gas flow direction may be an oxidation catalytic converter device, following which may be, for example, a particle filter device. An SCR (selective catalytic reduction) catalytic converter unit may be arranged further downstream. Because such a catalytic converter unit, especially a catalytic converter unit comprising an oxidation catalytic converter device, shall have a defined minimum temperature of about 200° C. for an efficient catalytic reaction, the problem is basically that a comparatively long time may pass until the catalytic converter device reaches this minimum temperature or reaches it again after a start-up or restart of the internal combustion engine, for example, after a so-called coasting mode of a vehicle.
In order to shorten this time, it is, for example, possible to arrange the catalytic converter unit as close as possible to an internal combustion engine in order thus to keep the heat loss from internal combustion engine exhaust gas leaving the internal combustion engine as minimal as possible on the flow path to the catalytic converter unit. However, this is often achieved with difficulty only because of the available space for installation in vehicles. Furthermore, an electric heater may be associated with such a catalytic converter unit. This catalytic converter unit can be put into operation when the catalytic converter device of same has a temperature that is too low. However, the operation of such an electric heater leads to a comparatively high load on the vehicle electrical system. Further, it is known that the thermal insulation of such an exhaust system can be improved with comparatively high design effort in order to thus guarantee an as fast as possible heating of a catalytic converter device due to reduced dissipation of heat to the surrounding area. In addition to the high design effort and thus also related cost, such a thermal insulation leads to the problem that a longer operation of an internal combustion engine in a high state of load may lead to a thermal overload of a catalytic converter unit. The result of such a thermal overload may be that the housing of the catalytic converter unit carrying the catalytic converter device expands to a comparatively great extent, while a catalytic converter device, which is constructed with ceramic material and is held in the housing with insertion of a fiber mat, does not expand thermally or expands thermally with considerably less intensity. Because of lost clamping action in the housing, this may lead to a displacement of the catalytic converter device in the direction downstream to a funnel-like-shaped outlet area for the internal combustion engine exhaust gas. If the housing subsequently cools off, this may lead to an excessive radial load and damage to the catalytic converter device.